I've recently purchased the audioinjector stereo soundcard for my Raspberry Pi Model 3 B+. I set up everything and I'm trying to record with jackd and a 16kHz sampling rate but it doesn't seem to be working. Specifically I get these ALSA errors when I try to start the jackd server:
ALSA: cannot set hardware parameters for capture
ALSA: cannot configure capture channel
Cannot initialize driver
JackServer: :Open failed with -1
Failed to open server

However, the jack server starts successfully with 48kHz sampling rate for example, isn't the 16kHz sampling rate supported by the audioinjector sound card? I've also updated everything and with my previous cirrus audio card I was able to record at 16kHz sampling rate.

I'm just using arecord to test functionality, my actual use is with a Golang ALSA library that doesn't have re-sampling functionality. I need to record frequencies up to 4kHz and the smallest file size is preferable. I was initially hoping to record in 8kHz directly but I've read the other forum post:viewtopic.php?f=5&t=3108

about it requiring kernel hacking which I was able to do but it still isn't optimal for my use. Reverting to a previous kernel version is also not an option in my case.

Recording in 16kHz and down-sampling 2x is the next best option, I'll just have to implement down-sampling in the Go library. It seems that the 16kHz issue isn't the same as the 8kHz one because I tried your suggestion of reverting the firmware to 4.9.25 and that fixed the 8kHz rate but not the 16kHz. The 16kHz rate didn't work after kernel hacking to modify the i2s driver either. Do you think it would be possible to find a way to get 16kHz to work with the current i2s driver?

I still haven't achieved running the jackd server with 16kHz sampling rate using the audioinjector card. For me reverting the firmware is not an option right now but it's really annoying that the soundcard can't work with 16kHz sampling rate (while the cirrus audiocard works fine). Have you found any solutions so far?

EDIT: The plughw option works for the jackd server but the quality of the sound input is terrible...
Apart from this, I tried portaudio and it seems to be working for 16kHz.

I tried changing the kernel of raspberry pi as in here, hoping to get 16kHz sampling rate to work on the audioinjector:viewtopic.php?f=5&t=3108
After this, I managed to get jackd to start with 8kHz and 16kHz. However, when I connect the microphone input to the playback (with jack_connect) the sound output that I get is terrible and also works for only one speaker.
I am still trying to understand why the cirrus audio card works just fine with 16kHz and the audioinjector fails. I tried also changing the kernel file according to the one corresponding to the rpi cirrus but I get the same result.

If anyone has found a solution for this, please share it. The support for the audioinjector is terrible so far so in case nobody bothers to find a solution for this the sound card will still be useless.